A novel polymer-based multiwall carbon nanotube (MWCNT) with high shielding effectiveness (SE) for use in packaging a 2.5-Gb/s plastic transceiver module is demonstrated. The MWCNT composites are tested to evaluate the electromagnetic (EM) shielding against emitted radiation from the optical transceiver modules. The results show that the SE of MWCNT composite packages exhibit 38-45 dB in the far-field source and 28-40 dB in the near-field source at a frequency range of 1-3 GHz, and an average of 14 dB for the optical transceiver modules at a frequency of 2.5 GHz. The MWCNT composites with their high SE are potentially suitable for packaging low-cost and low-EM-interference optical transceiver modules used in Gigabit Ethernet or fiber-to-the-home lightwave transmission systems